There are many references in the literature to the chemical cleaning of solid carbonaceous material. While most of these references are directed to coal, it is to be understood that the term "solid carbonaceous material" includes petroleum coke, metallurgical coke, charcoal, other products of coal pyrolysis, and solid products of coal hydrogenation, as well as coal. The primary objective of these processes is to remove sulphur from the solid carbonaceous material. For the purposes of this patent application the discussion of the prior art and the invention will be described in conjunction with coal but it is to be understood that it is applicable to petroleum coke and charcoal and any other solid carbonaceous materials.
One or more problems associated with the desulfurization of coal based on treatment with gases at elevated temperatures involve the loss of the heating value of the coal, the corrosive reaction conditions required, long reaction times, the need for high temperatures and pressures, the high consumption of hydrogen, waste disposal problems, the relatively small amounts of sulphur removed from the coal, and the inability to market the treated coal.
The use of ethanol to remove sulfur from coal, disclosed in U.S. Pat. No. 4,888,029, Shiley, et al, overcomes some of the disadvantages of earlier chemical processes. However, the yield obtained by this process upon scale-up does not make it economically attractive.
According to U.S. Pat. No. 4,888,029, which is a one-stage process, in the conditions of this patent (300.degree.-500.degree. C.; flowing inert gas containing 0.5-2% reaction accelerator) ethanol is dehydrogenated at the surface of pyrrhotite and/or troilite (FeS) formed from the pyrite in the coal to release atomic hydrogen which reacts with both the sulfur in the pyrrhotite and the troilite and with the organic sulfur (which is chemically bonded in the coal and very difficult to remove) to form gaseous hydrogen sulfide (H.sub.2 S) and acetaldehyde in accordance with the following reactions: ##STR1##
However, reaction (2) is not thermodynamically favorable in the conditions of the method of U.S. Pat. No. 4,888,029 (400.degree.-500.degree. C.) and requires a very low concentration of H.sub.2 S in the reaction bed (less than 300 ppm) to proceed forward. Such a low H.sub.2 S concentration is not attainable in the conditions of the method of this patent. In addition, reactions (1) and (3) are not sufficiently catalytically activated.